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            <div><h4 class="title">
                <a name="asio.overview.windows.random_access_handle"></a><a class="link"
                                                                            href="random_access_handle.html"
                                                                            title="Random-Access HANDLEs">Random-Access
                HANDLEs</a>
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    <p>
        Asio provides Windows-specific classes that permit asynchronous read and
        write operations to be performed on HANDLEs that refer to regular files.
    </p>
    <p>
        For example, to perform asynchronous operations on a file the following
        object may be created:
    </p>
    <pre class="programlisting"><span class="identifier">HANDLE</span> <span class="identifier">handle</span> <span
            class="special">=</span> <span class="special">::</span><span class="identifier">CreateFile</span><span
            class="special">(...);</span>
<span class="identifier">windows</span><span class="special">::</span><span
                class="identifier">random_access_handle</span> <span class="identifier">file</span><span
                class="special">(</span><span class="identifier">my_io_context</span><span
                class="special">,</span> <span class="identifier">handle</span><span class="special">);</span>
</pre>
    <p>
        Data may be read from or written to the handle using one of the <code class="computeroutput"><span
            class="identifier">read_some_at</span><span class="special">()</span></code>,
        <code class="computeroutput"><span class="identifier">async_read_some_at</span><span
                class="special">()</span></code>,
        <code class="computeroutput"><span class="identifier">write_some_at</span><span class="special">()</span></code>
        or <code class="computeroutput"><span class="identifier">async_write_some_at</span><span
            class="special">()</span></code> member functions. However, like the equivalent
        functions (<code class="computeroutput"><span class="identifier">read_some</span><span class="special">()</span></code>,
        etc.) on streams, these functions are only required to transfer one or
        more bytes in a single operation. Therefore free functions called <a class="link"
                                                                             href="../../reference/read_at.html"
                                                                             title="read_at">read_at()</a>, <a
            class="link" href="../../reference/async_read_at.html" title="async_read_at">async_read_at()</a>,
        <a class="link" href="../../reference/write_at.html" title="write_at">write_at()</a> and <a class="link"
                                                                                                    href="../../reference/async_write_at.html"
                                                                                                    title="async_write_at">async_write_at()</a>
        have been created to repeatedly call the corresponding <code class="literal"><span
            class="bold"><strong>*</strong></span>_some_at()</code> function until all data has
        been transferred.
    </p>
    <h6>
        <a name="asio.overview.windows.random_access_handle.h0"></a>
        <span><a name="asio.overview.windows.random_access_handle.see_also"></a></span><a class="link"
                                                                                          href="random_access_handle.html#asio.overview.windows.random_access_handle.see_also">See
        Also</a>
    </h6>
    <p>
        <a class="link" href="../../reference/windows__random_access_handle.html" title="windows::random_access_handle">windows::random_access_handle</a>.
    </p>
    <h6>
        <a name="asio.overview.windows.random_access_handle.h1"></a>
        <span><a name="asio.overview.windows.random_access_handle.notes"></a></span><a class="link"
                                                                                       href="random_access_handle.html#asio.overview.windows.random_access_handle.notes">Notes</a>
    </h6>
    <p>
        Windows random-access <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
        are only available at compile time when targeting Windows and only when
        the I/O completion port backend is used (which is the default). A program
        may test for the macro <code class="computeroutput"><span class="identifier">ASIO_HAS_WINDOWS_RANDOM_ACCESS_HANDLE</span></code>
        to determine whether they are supported.
    </p>
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